“I am aware that I and no church authority may endorse candidates for political office,” Father Farren wrote.

You could practically see him winking.

Father Farren proceeded to turn over much of his page in the bulletin to a letter written by six former ambassadors to the Vatican who said they were supporting Mitt Romney for president because of his opposition to abortion, to marriage rights for same-sex couples and to aspects of the national health insurance law that require coverage of contraceptives.

“We urge our fellow Catholics, and indeed all people of good will to join with us in this full-hearted effort to elect Gov. Mitt Romney as the next President of the United States,” concluded the Romney supporters.

As it happened, just as the weekly bulletin appeared in the pews at St. Catherine’s, the head of the New York Archdiocese, Cardinal Timothy M. Dolan, was getting ready to head for Charlotte, N.C. There, he would give a prayer at the close of the Democratic National Convention, just as he had in Tampa, Fla., where Republicans met to formally select Mr. Romney as their nominee. It was a conspicuous display of even-handedness.

Father Farren was filling in for the parish’s pastor, who was taking a break on Labor Day weekend. Normally, church bulletins do not become hot items. But more than 20,000 people signed a petition to Cardinal Dolan, objecting to Father Farren’s endorsement-by-proxy. Though it was the voice of one priest, and not the institutional church, it opened a window onto a debate among Catholics about how they and the church engage with civil society. The church has made strong statements about economic justice for the poor, protection of immigrants, support of labor unions and objections to the death penalty, but those issues have largely been drowned out by advocacy against abortion and same-sex marriage.

“We have a responsibility to be engaged in the public debate,” said James Salt, the leader of Catholics United, a group that supported the petition drive and that promotes what it views as the overlooked aspect of Catholic social justice doctrine. “If the church wants to be a spiritual leadership in our culture, they can’t be seen as the heirs of Pat Robertson and Jerry Falwell.”

The church bulletin was sent by a man who attended Mass at St. Catherine’s to a group called Americans United for Separation of Church and State, which filed a complaint with the Internal Revenue Service.

Tax-exempt organizations like churches are “absolutely prohibited from directly or indirectly participating in, or intervening in, any political campaign on behalf of (or in opposition to) any candidate for elective public office,” according to I.R.S. guidelines. This includes, according to the I.R.S., “distributing statements prepared by others that favor or oppose any candidate for public office.”

The petitions from Catholics United were delivered to St. Patrick’s Cathedral last week. “I wouldn’t comment beyond noting that archdiocesan policy is clear that our churches should not endorse candidates for office,” said Joseph Zwilling, a spokesman for the archdiocese.

On Tuesday morning, about 25 people gathered for Mass at St. Catherine’s. The church, an imposing presence that stretches from 68th Street to 69th Street, and is close to four major medical centers, was nearly empty. The least sound rose into vaulted ceilings, gathered force and carried to the most distant pew: a squeak of rubber soles, the clink of a coin dropped in an offering box.

At the rear of the church was a stack of fresh church bulletins, these carrying a note from the Rev. Jordan Kelly, the church pastor, about the letter.

“The reprinting of this letter was an unfortunate error in judgment,” Father Kelly wrote. He regretted the confusion.

During the Mass, another priest, Juan-Diego Brunetta, prayed for “the sick and dying in the hospitals all around us, especially those who will die this day.”

In one aisle, a hospital housekeeper, in a blue pinstriped dress, bowed her head. The Mass finished early enough for her and other hospital workers to get to work on time without politics, but with faith and reason braided into a rope to use while crossing the slippery deck of the day.

Correction: September 20, 2012

The About New York column on Wednesday about an endorsement of Mitt Romney for president that was printed in Manhattan’s Church of St. Catherine of Siena bulletin, misstated the surname of the leader of Catholics United, a group that supported a petition drive objecting to the action. He is James Salt, not Salter.

E-mail: dwyer@nytimes.com

Twitter: @jimdwyernyt

A version of this article appears in print on September 19, 2012, on page A23 of the New York edition with the headline: Priest’s Dip Into Politics Raises Outcry. Order Reprints|Today's Paper|Subscribe